Collector potential



Sept. 27, 1960 J. M. EARLY SEMICONDUCTOR SIGNAL TRANSLATING DEVICESOriginal Filed Dec. 16, 1952 FIG. 3

5 6 THICKNESS OF ZONE ll (IO' CM) 5 4 3 2 l O $3 9 QEEEE mwqwm O 24 6 8lO -|2 I4 l6 182022 COLLECTOR PO TEN T/AL COLLE C TOR PO TEN T/ALINVENTOR By J. M. EARL Y ATTORNEY United tates atent Re. 24,82 2*Reissued Sept. 27, 1960 SEMICONDUCTOR SIGNAL TRANSLATIN G DEVICES JamesM. Early, Summit, N.J., assignor to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Original No.2,767,358, dated (let. 16, 1956, Ser. No. 326,312, Dec. 16, 1952.Application for reissue Feb. '3, 1958, Ser. No. 713,074

9 Ciairas. (Cl. 317-235) Matter enclosed in heavy brackets I] appears inthe original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

This invention relates to semiconductor signal translating devices ofthe type now known as transistors and more particularly to junctiontransistors.

Junction transistors, such as illustrated in Patent 2,569,347, grantedSeptember 25, 1951, to W. Shockley, comprise, in general, a body ofsemiconductive material, such as germanium or silicon, having therein azone of one conductivity type between and defining junctions with a pairof zones of the opposite conductivity type. Individual substantiallyohmic connections are made to the zones, that to the intermediate zonebeing termed the base and those to the outer zones being designated theemitter and collector respectively. The properties of such devices arediscussed in an article by R. L. Wall-ace and W. J. Pietenpol in theBell System Technical Journal, July 1951, page 530.

Of particular moment among the performance characteristics of junctiontransistors are the current multiplication factor, commonly designatedalpha, and the operating frequency range, more particularly thefrequency range over which at least a prescribed gain is realizable.Also of particular moment are the power capacity and operatingstability.

One general object of this invention is to improve the performancecharacteristics 04: transistors.

More specifically, objects of this invention are to enhance the gain andoperating frequency range of transistors, to increase the power capacitythereof, to improve the stability of such devices and to facilitate theconstruction of junction transistors.

In accordance with one feature of this invention, the semiconductivebody of a transistor is constructed tooptimize the base resistance andcollector capacitance whereby, inter alia, substantial gain over a widefrequency range is attained. More specifically, in accordance with onefeature of this invention, a region of the semiconductive body in atransistor, between the base and collector, is constructed to have ahigh resistivity, specifically substantially intrinsic conductivity, andthe base layer or zone is constructed to have a very low resistivity.Consequently, both a low base resistance and a low collector capacitanceare attained and this, it has been determined, leads to substantialenhancement of the performance characteristics of the device.

Particularly advantageously, the body is formed as a single crystalhaving therein a pair of contiguous zones, one of which is of theconductivity type desired for the base region and the other of which isof substantially intrinsic conductivity. The emitter and collector zonesof a junction transistor are produced by introduction of an appropriateimpurity into portions of the base and intrinsic zones thereby to createin these zones islands or layers of the conductivity type opposite thatof the base zone.

In operation of the device, the emitter is biased in the forwarddirection and the collector in the reverse direction, both relative tothe base. Because of the reverse bias on the collector, a space changeor barrier region obtains between the base and collector and this, byvirtue of the presence of the substantially intrinsic region, can bemade to extend from the collector to the bme at a relatively lowcollector voltage. Further, barrier regions of substantial width,leading to low collector capacitances, are realizable.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 depicts diagrammatically a junction transistor illustrative ofone embodiment of this invention;

*Fig. 2 portrays another illustrative embodiment of this invention; and

Figs. 3, 4 and 5 are graphs representing relations of certain parametersof particular moment in the opera tion of transistors constructed inaccordance with this invention.

In the drawing, for the sake of clarity of illustration, thesemiconductive body has been shown to a greatly enlarged scale. Intypical devices, this body may be .00l.l00 inch by 1001-10 inch in crosssection, the base zone maybe of the order of 4x 10 -10 inch thick andthe substantially intrinsic region may be of the order of 2.5 X 1() -51O inch thick. Also in the drawing, the conductivity type of each of theseveral zones is designated by 'the identifying letter, N, I or P.

Referring now to the drawing, the translating device portrayed in Fig. 1comprises a disc or wafer 10 of semieonductive material, such as siliconor germanium, having therein a substantially intrinsic zone 11 and azone 12 strongly of one conductivity type, for example N type asindicated. The disc or wafer 10 comprises also two zones 13 and 14strongly of the conductivity type opposite rthat of the zone 12, forexample P type as indicated. The zones. 12, 13 [and 14 constitute thebase, emitter and collector regions respectively of the transistor andhave ohmic connections thereto.

In operation of the device, the junction between the base and emitterregions 12 and 13 is biased in the forward direction as by a battery 17and signals as from a source 1 8 are impressed between these tworegions. The collector zone 14 is biased in the reverse direction withrespect to the base as by battery 15 in series with a load representedgenerally by the resistor 16.

Advantageously the semiconductive disc 01' water is of single crystalconstruction fabricated for example in the manner disclosed in theapplication Serial No. 168,184, filed June 15, 1950, of G. K. Teal, nowPatent 2,727,840 issued December 20-, 1955, the N zone 12 being producedby heavily doping a melt of substantially intrinsic material with asignificant impurity such as antimony. The P regions 13 and 14 may beproduced by alloying an acceptor impurity such as indium with theintrinsic and N type zones- 11 and 12, respectively, as in the mannerdisclosed in the application Serial No. 270,370, filed February 7, 1952,of G. L. Pearson.

Advantageously, the zones 12, 13 and 114 are strongly extn'nsic whereby,inter alia, a low base resistance is obtained, a copious supply ofmajority carriers is provided at the emitter zone 13 for injection intothe base zone 12, and relatively high temperature insensitivity isrealized at the collector. For example, in a typical device wherein thesemiconductive material is germanium, the base zone 12 may have aresistivity of the order of .001-10' ohm centimeter and the emitter andcollector zones 13 and 14 may have a resistivity of the order of or lessthan .001 ohm centimeter.

In the substantially intrinsic zone 11, however, the donors andacceptors are substantially in balance so that the excess carrierconcentration is very small and the resistivity is high. Advantageously,the resistivity is greater than 30 ohm centimeter.

In operation of the device, advantageously the reverse bias upon thecollector zone 14 is such that a space charge or barrier region extendsthrough the intrinsic zone 11, that is bridges the space between thebase and collector zones. As is now known, even for zero bias, anelectrostatic potential obtains across each of the junctions between theintrinsic zone 11 and the base and collector zones 12 and 14. The sum ofthese. and the collector bias requisite to extend the barrier regionfrom base to collector is herein termed the barrier potential. Therelation between the latter and thickness or width of the zone 11 isportrayed in Fig. 3 or several values of excess carrier concentration orresistivity for the zone 11 in germanium. Specifically, in this figure,curve A portrays the relation for a zone 11 having a resistivity ofabout 30 ohm centimeters corresponding to an excess carrierconcentration of about 3 1O /cc., curve B represents the case for a Zone11 of about 45 ohm centimeters resistivity, corresponding to an excesscarrier concentration of about /cc. and curve C shows the relation for azone 11 wherein the excess carrier concentration is about 3 X10 It willbe noted from Fig. 3 that for a device wherein the zone 11 has theproperties corresponding to curve C, a barrier potential of only about 5volts is required when the zone 11 is about 5 X 1() centimeters thick orwide.

The condition of a barrier region bridging the substantially intrinsiczone not only is obtainable at a relatively small collector bias, aspointed out hereinabove, but also obtains without substantial changewith variations in the collector potential. Further, this is realizedwithout deleterious diminution in the thickness of the base zone 12. Asdepicted by curve D in Fig. 4, in a device, such as represented in Fig.1, wherein the semiconductive body is of PNIP configuration, the barrierwidth increases with collector potential up to a certain potentialcorresponding to the barrier potential, and then remains substantiallyconstant. For a body of PNP configuration, however, as illustrated bycurve E, the barrier width increases continuously with collectorpotential. Thus, devices constructed in accordance with this inventionenable realization of high operating stability.

As portrayed by curve F in Fig. 5, in a PNIP transistor such as shown inFig. 1, the effective width of the base decreases with collectorpotential until the barrier potential value is reached and thereafterremains substantially constant. For a PNP transistor, however, asindicated by curve G, the base width decreases with increasing collectorpotential until the width becomes zero, that is break through of thebase zone occurs. Thus, as is evident, devices constructed in accordanceWith this invention enable operation at higher power levels than heretofore attainable without failure of the transistor.

Further, it has been found that in operation of transistors the gain athigh frequencies is dependent upon the collector capacitance, the baseresistance and the collector bodyresistance. Specifically, in order thatgain may be maintained at high frequencies, it is advantageous that theproduct of the collector capacitance by the sum of the base resistanceand the collector body resistance be small. In devices constructed inaccordance with this invention, by virtue of the intrinsic region, asmall collector capacitance is obtained. Also both the base resistanceand collector body resistance may be made small readily. Thus, theproduct above noted is small and high. gain over a wide frequency rangeis realized. Further, it will be appreciated that each of the threeparameters involved is amenable to design control so that the relationtheerof may be optimized to provide a prescribed operatingcharacteristic, such, for example, as gain of at 4 least a certainmagnitude over a specified band of frequencies.

The invention may be embodied also in transistors including one or morepoint contacts. In one construction, illustrated in Fig. 2, the emitteris a point contact 130 bearing against the base zone 12 and thecollector is a point contact bearing against the intrinsic region 11.Advantageously, the collector connection is formed electrically in waysnow well known in the art. It will be understood also, of course, thatthe invention may be utilized in junction emitter-point collector andpoint emitter-junction collector transistors.

Ideally intrinsic semiconductive material, that is such wherein thedonors and acceptors are exactly in balance, is not essential to therealization of the advantages of devices constructed in accordance withthis invention.

That is to say, the substantially intrinsic region I may be eitherslightly N or P type, say exhibiting an excess concentration of carriersof the order of 5 10 or having a resistivity of about 30 ohm centimetersor higher. Advantageously, the sign of the excess charge is such as toneutralize the space charge of the mobile carriers which carry theconduction current to the collector region. Thus, :for a body of PNIPconfiguration such as illustrated in Fig. 1, the substantially intrinsicregion may be slightly P type thereby to neutralize the space charge dueto the holes injected into the base region or zone 12 from the emitterzone '13 and drawn toward the collector Zone 14. The neutralization ofspace charge thus effected increases the current obtainable at a givenvoltage or conversely reduces the voltage requisite to obtain aprescribed current.

Although the invention has been described with particular reference totransistors including a semiconductive body of PNIP configuration, itmay be utilized also in devices wherein this body is of NPINconfiguration. Also, it will be understood that the embodiments of theinvention shown and described are but illustrative and that variousmodifications may be made therein without departing from the scope andspirit of this invention,

What is claimed is:

1. A signal translating device comprisin: a body of semiconductivematerial having therein a first zone of substantially intrinsicconductivity and a second zone of extrinsic conductivity and of oneconductivity type contiguous with said first zone, a substantiallyrectifying collector connection directly to said first zone, and asubstantially nonrectifying base connection and one substantiallyrectifying emitter connection both directly to said second zone, wherebylow collector to base capacity is achieved.

2. A signal translating device in accordance with claim 1 wherein saidemitter connection comprises a zone in said body of a conductivity typeopposite to that of said extrinsic zone and said collector connectioncomprises another zone of said opposite conductivity type in said bod 3.A signal translating device in accordance with claim 1 wherein each ofsaid emitter and collector connections comprises a point contact.

4. A signal translating device in accordance with claim 1 wherein saidemitter connection comprises a zone in said body of a conductivity typeopposite to that of said extrinsic zone and said collector connectioncomprises a point contact.

5. A signal translating device in accordance with claim 1 wherein saidemitter connection comprises a point contact and said collectorconnection comprises a zone n said body of a conductivity type oppositeto that of said extrinsic zone.

6. A semiconductor device comprising a body of crystalline semiconductormaterial consisting of a plurality of layers of semiconductor materialsincluding in order a first layer of one type of conductivity material, asecond of material of the same type of conductivity as said secondlayer, said second layer having a higher conductivity than said thirdlayer, and a fourth layer of material of the same type of conductivityas said first layer.

7. A semiconductor device comprising a body of crystalline semiconductormaterial having an emitter semiconauctor region and a collectorsemiconductor region of the same conductivity type material, a baseregion of opposite conductivity type material interposed between saidtwo regions and separated therefrom by rectifying barriers, said baseregion including two layers of difierent magnitude of conductivity, thelayer of lower conductivity being adjacent to said collector region andthe layer of higher conductivity being adjacent to said emitter region.

8. A semiconductor device comprising a body of crystalline semiconductormaterial consisting of a plurality of layers of semiconductor materialsselected from the class consisting of germanium and silicon including inorder a first layer of one type of conductivity material, a second layerof opposite conductivity type material, a third layer of material of thesame type of conductivity as said second layer, said second layer havinga higher conductivity than said third layer, and a fourth layer ofmaterial of the same type of conductivity as said first layer.

9. A semiconductor device comprising a body of crystalline semiconductormaterial selected from the class consisting of germanium and siliconhaving an emitter semiconductor region and a collector semiconductorregion of the same conductivity type material, a base region of oppositeconductivity type material interposed between said two regions andseparated therefrom by rectifying barriers, said base region includingtwo layers of different magnitude of conductivity, the layer of lowerconductivity being adjacent to said collector region and the layer ofhigher conductivity being adjacent to said emitter region.

References Cited in the file of this patent or the original patentUNITED STATES PATENTS

